Shiny curtains of hair, a headful of voluptuous curls, bouncy ends that don't split—hair inevitably loses its youthful zest over the years, but new products can help recapture the past.

"How beautiful is youth! How it gleams with illusions, aspirations, and dreams!" Had Henry Wadsworth Longfellow been a woman, he almost certainly would have added "shiny hair" to that list. Think of the waist-long mane you had when you were a teenager—shiny, strong, resilient. Over the years, hair, like skin, starts to show its age—and by your 30s, dullness, dryness, breakage, and thinning set in.

Hair, of course, is dead. But that doesn't mean it's not affected by the passage of time. "As you get older, the cells on your body don't reproduce quite as fast," says Neil S. Sadick, clinical professor of dermatology at Weill Cornell Medical College in New York City. "That's true of hair cells as well. The active cells around the follicle aren't as strong, so over the years, hair becomes finer, duller, and weaker. It's just the natural course of life."

Although there's no such thing as Botox for hair, there are temporary solutions that help. "Products can do more today than ever before to firm the hair fibers and make the hair stronger," says Wilma Bergfeld, a dermatologist at the Cleveland Clinic in Ohio. "Advances have been made in combining ingredients that have not been combined before." For example, protein conditioners are now mixed with amino acids that are small enough to penetrate the hair shaft, which increases their ability to strengthen hair. Sounds like poetry to us.

PROBLEM: THINNING

It's a good thing Rapunzel was only 12 when she got stuck in the tower—had she been much older, her hair wouldn't have been thick enough to climb. Nothing can turn sparse hair into an abundant mane, but using Rogaine twice a day, which stimulates the follicle, can slow down hair loss and promote growth. And studies have shown that LED light activates the cells in the follicle that grow hair.

Supplements can also beef up thin strands. "There's a lot of science that vitamins that are good for skin—antioxidants, vitamin B, calcium, zinc, and iron—also promote healthy hair," says Bergfeld. "Biotin and niacin can do wonders for hair in a weakened state, but you don't get enough from regular multivitamins." Doctors recommend at least 1,000 micrograms of biotin and 500 milligrams of niacin a day.

At the very least, shampoos and conditioners created for fine or thinning hair can give the appearance of thickness. They coat the hair with a positive electric charge that adheres to the hair's negative charge, creating more space between each strand, which makes hair look fuller. Mousse, styling spray, and aerosol hair spray can also create fullness by lifting hair at the root. Heat-activated products, for their part, prevent damage and "seal conditioners into the hair fiber, which makes the hair thicker and firmer," says Bergfeld.

A quick style modification can work, too. As opposed to a wispy cut, thick bangs with slightly uneven ends create the illusion of more hair. If they start to look stringy as they grow out, a dry shampoo will help plump them up.

PROBLEM: FLAT/LIMP

For every stylist who says your hair looks better dirty, there's a dermatologist who wants you to wash it. Hair not only gets finer with age, but it also turns limp—and oil weighs it down more. Sadick suggests washing hair as soon as it feels oily, typically every day to every third day depending on texture (straight hair needs to be washed more often than curly).

Hair as limp as overcooked noodles can look fuller with well-placed layers. "The length doesn't change, but a few sections in the back and around the face that fall two or three inches shorter than the ends will add volume," says Chris McMillan, owner of Chris McMillan, The Salon in Beverly Hills. "Don't layer your whole head—that's '90s newscaster hair. And get regular trims, because healthy ends make hair appear thicker."

For layers to reach their full potential, you need to style them properly. When hair is damp, spray the layers around your face with styling lotion, flip all the hair over the opposite ear, and dry the roots from underneath. But sometimes the simplest solution is the most effective: Switching your part to the other side will instantly perk up lank hair.

PROBLEM: DULLNESS

"Remember the Archie and Veronica comic?" asks cosmetic chemist Mort Westman. "Veronica had that white bar across the top of her hair where the light was reflecting. That's what we lose when we age." Styling and general wear and tear cause the cuticle of the hair shaft to fray and reflect light unevenly. The key is to get the cuticle to lie flat again. Look for shampoos and conditioners with silicone, usually seen on the label as dimethicone, and shine sprays, serums, and drops that contain silicones. "The silicone products are lighter than oil-based ones, giving great shine without weighing the hair down," says cosmetic chemist Jim Hammer.

If your hair is still the dull greige of an old sofa, color can save the day (or at least your appearance). Colorist Kim Vo, owner of the Kim Vo Salons in Beverly Hills and Las Vegas, applies a tint that matches hair's natural shade, leaving it on for only 30 seconds. "It gives the tiniest kick of color and makes the hair slightly richer," he says. Highlights can also make hair gleam like a new car. Vo suggests getting them around the face in one shade lighter than your natural color.

PROBLEM: DRYNESS AND DAMAGE

Split ends appear at about the same time a woman opens her first checking account—and they don't go away. Environmental toxins cause breakage, as do brushing, blow-drying, ironing, curling, and coloring. Dermatologist Doris J. Day offers a test for assessing the damage: "Use both hands to pinch a strand of hair in two places, then pull. If it breaks easily and the broken ends don't curl up, you have damage."

Using a shampoo that's designed for dry, damaged hair can help. They're typically packed with moisturizing ingredients, as well as lipids and other proteins that won't strip hair. "They may also contain various cationic polymers that adhere to the hair and are useful for strengthening and repairing damaged areas," says Hammer.

Damage-specific conditioners pick up where shampoos leave off. "They are very moisturizing and contain polymers and silicone-type ingredients. These give hair a long-lasting, flexible, smooth coating to resist damage from styling, and they can sometimes repair split ends," says Hammer, who recommends a leave-in conditioner for hair that's especially beat-up. Anti-frizz serums are the last step—they smooth hair.

But as with a tanking stock, sometimes you've got to cut your losses. "Snip one or two inches from the bottom and trim the layers around your face," says McMillan. From there, practice safe styling. Blow-dry hair when it's damp, not wet, and once it's dry, work two or three drops of silicone serum into the ends of the hair. If you want to straighten hair, use a ceramic flatiron, which is gentler than a metal one. "Heating tools smooth the cuticle so it looks shinier and smoother," says McMillan. Women with long, fine hair should skip the flatiron. After all, mall rat is not the kind of youthful look we're after.